Organic electroluminescent device

ABSTRACT

An organic electroluminescent device comprising: a pair of electrodes; and at least one organic layer between the pair of electrodes, the at least one organic layer between the pair of electrodes, the at least one organic layer including a luminescent layer, wherein the luminescent layer contains at least one electron injection/transport compound, at least one hole injection/transport compound, and at least one green or blue phosphorescent compound; and the electron injection/transport compound and the hole injection/transport compound each has a minimum triplet exciton energy value which is equal to or more than that of the green or blue phosphorescent compound.

TECHNICAL FIELD

The present invention relates to a luminescent device capable ofconverting electric energy to light to cause light emission,particularly an organic electroluminescent device and to an organic ELdevice that can be suitably utilized in the fields including displayelement, display, backlight, illumination light source, recording lightsource, exposure light source, reading light source, sign, signboard,interior, and optical communication.

BACKGROUND ART

In recent years, active research and development regarding organicelectroluminescent devices (the organic electroluminescent device beingsometimes referred to as “luminescent device”, “organic EL device”, or“EL device” in the invention) are carried out because light emissionwith a high luminance is obtained at low-voltage driving. In general,the organic EL device is constituted of counter electrodes having aluminescent layer or a plurality of organic layers containing aluminescent layer put therebetween. The organic EL device utilizes lightemission from excitons formed by recombination of electrons injectedfrom a cathode and holes injected from an anode in a luminescent layer,or utilizes light emission from excitons of other molecule formed byenergy transfer from the foregoing excitons.

In an organic luminescent device comprising an anode, a cathode and anorganic compound film, there is reported an organic luminescent devicein which the organic compound film includes a hole transport regioncomprising a hole transport material and an electron transport regioncomprising an electron transport layer, a mixed region containing boththe hole transport material and the electron transport material isprovided between the hole transport region and the electron transportregion, and a material capable of causing red light emission from thetriplet excitation state is added in the mixed region (see, for example,JP-A-2002-305085). However, any means for improving efficiency anddurability of blue and green EL devices is not disclosed at all.

DISCLOSURE OF THE INVENTION

An object of the invention is to provide a green or blue EL devicehaving good luminous efficiency and durability. Another object of theinvention is to provide a green or blue EL device having good luminousefficiency and durability using a specific compound in a luminescentlayer.

The foregoing problems have been attained as follows.

(1) An organic electroluminescent device comprising a pair of electrodeand at least one organic layer including a luminescent layertherebetween, wherein the luminescent layer contains at least oneelectron injection/transport compound, at least one holeinjection/transport compound, and at least one green or bluephosphorescent compound; and the electron injection/transport compoundand the hole injection/transport compound each has a minimum tripletexciton energy value (T₁ value) is equal to or more than that of thegreen or blue phosphorescent compound.

(2) The organic electroluminescent device as set forth above in (1),wherein the hole injection/transport compound has an ionizationpotential (Ip value) of from 5.6 eV to 6.1 eV.

(3) The organic electroluminescent device as set forth above in (1) or(2), wherein the electron injection/transport compound has an electronaffinity (Ea value) of from 2.0 eV to 3.5 eV.

(4) The organic electroluminescent device as set forth above in any oneof (1) to (3), wherein the green or blue phosphorescent compound is atransition metal complex capable of emitting light via the tripletexcitation state.

(5) The organic electroluminescent device as set forth above in any oneof (1) to (4), wherein the electron injection/transport compound, thehole injection/transport compound and the green or blue phosphorescentcompound each has a T₁ value of 62 kcal/mole (259 kJ/mole) or more; andphosphorescence obtained from the green or blue phosphorescent compoundhas a λmax (emission maximum wavelength) of not longer than 500 nm.

(6) The organic electroluminescent device as set forth above in any oneof (1) to (5), wherein the hole injection/transport compound is asubstituted or unsubstituted pyrrole compound.

(7) The organic electroluminescent device as set forth above in (6),wherein the substituted or unsubstituted pyrrole compound is representedby the following formula (1).

In the formula, R¹¹, to R¹⁵ each represents a hydrogen atom or asubstituent, and the substituents may be bonded to each other to form aring structure.(8) The organic electroluminescent device as set forth above in (7),wherein the formula (1) is represented by the following formula (3).

In the formula, R³² to R³⁵ are synonymous with R¹² to R¹⁵, respectively;L³¹ represents a connecting group; L³² represents a di- or more valentconnecting group; n³² represents an integer of 2 or more; and n³²represents an integer of from 0 to 6.

(9) The organic electroluminescent device as set forth above in any oneof (1) to (5), wherein the electron injection/transport compound is aheterocyclic compound containing at least two nitrogen atoms.

(10) The organic electroluminescent device as set forth above in (9),wherein the heterocyclic compound containing at least two nitrogen atomsis a compound represented by the following formula (2).

In the formula, R²¹ represents a hydrogen atom or a substituent; X²¹,X²², X²³, and X²⁴ each represents a nitrogen atom or a substituted orunsubstituted carbon atom; and at least one X²¹, X²², X²³, and X²⁴represents a nitrogen atom.(11) The organic electroluminescent device as set forth above in (10),wherein the formula (2) is represented by the following formula (4).

In the formula, R⁴¹, R⁴², and R⁴³ each represents a hydrogen atom or asubstituent; L⁴¹ represents a connecting group; n⁴¹ represents aninteger of 2 or more; L⁴² represents a di- or more valent connectinggroup; and n⁴² represents an integer of from 0 to 6.(12) The organic electroluminescent device as set forth above in (10),wherein the formula (2) is represented by the following formula (5).

In the formula, R⁵², R⁵³, and R⁵⁴ each represents a hydrogen atom or asubstituent; L⁵¹ represents a connecting group; n⁵¹ represents aninteger of 2 or more; L⁵² represents a di- or more valent connectinggroup; and n⁵² represents an integer of from 0 to 6.

(13) The organic electroluminescent device as set forth above in (4),wherein the transition metal complex capable of emitting light via thetriplet excitation state is at least one member selected from an iridiumcomplex, a platinum complex, a rhenium complex, a ruthenium complex, apalladium complex, a rhodium complex, and a rare earth complex.

(14) The organic electroluminescent device as set forth above in any oneof (1) to (13), wherein the organic layer has at least three layers of ahole transport layer, a luminescent layer, and an electron transportlayer, and the electron transport layer has an Ip value of 5.9 eV ormore.

(15) The organic electroluminescent device as set forth above in any oneof (1) to (14), wherein the electron injection/transport compoundcontained in the luminescent layer is a compound different from thecompound contained in the electron transport layer.

(16) The organic electroluminescent device as set forth above in any oneof (1) to (15), wherein the hole injection/transport compound containedin the luminescent layer is a compound different from the compoundcontained in the hole transport layer.

(17) The organic electroluminescent device as set forth above in any oneof (1) to (16), wherein the electron injection/transport compoundcontained in the luminescent layer is a transition metal complex notcontaining a substituted or unsubstituted 8-hydroxyquinolinol in aligand thereof.(18) The organic electroluminescent device as set forth above in any oneof (1) to (17), wherein at least one of the hole injection/transportcompounds contained in the luminescent layer is represented by thefollowing formula (6).

In the formula, R⁶¹, R⁶² and R⁶³ each represent a substituent. n⁶¹ ton⁶³ each represent an integer of 0 to 5.(19) The organic electroluminescent device as set forth above in any oneof (1) to (18), wherein at least one of the hole injection/transportcompounds contained in the luminescent layer is represented by thefollowing formula (7).

In the formula, R⁷⁰ to R⁷⁹ each represent a hydrogen atom, an alkylgroup, an aryl group, or a group that forms a hydrocarbon ring whenbonded to each other.

(20) The organic electroluminescent device as set forth above in any oneof (1) to (19), wherein at least one of the electron injection/transportcompounds contained in the luminescent layer is a nitrogen-containingsix-membered ring compound.

(21) The organic electroluminescent device as set forth above in (20),wherein the nitrogen-containing six-membered ring compound isrepresented by the following formula (8), formula (9), formula (10) orgeneral formula (11).

In the formulae, R⁸¹ to R⁸⁵, R⁹¹ to R⁹⁴, R¹⁰¹ to R¹⁰⁴ and R¹¹¹ to R¹¹³each represents a hydrogen atom or a substituent.

(22) The organic electroluminescent device as set forth above in any oneof (1) to (21), wherein at least one of the electron injection/transportcompounds contained in the luminescent layer is a nitrogen-containingheterocyclic compound, and that at least one of the holeinjection/transport compounds is a pyrrole compound.

(23) The organic electroluminescent device as set forth above in any oneof (1) to (21), wherein at least one of the electron injection/transportcompounds contained in the luminescent layer is a nitrogen-containingheterocyclic compound, and that at least one of the holeinjection/transport compounds is a triarylamine-based compound.

(24) The organic electroluminescent device as set forth above in any oneof (1) to (21), wherein at least one of the electron injection/transportcompounds contained in the luminescent layer is a nitrogen-containingheterocyclic compound, and that at least one of the holeinjection/transport compounds is a hydrocarbon-based aromatic compound.

(25) The organic electroluminescent device as set forth above in any oneof (1) to (21), wherein at least one of the electron injection/transportcompounds contained in the luminescent layer is a hydrocarbon-basedaromatic compound, and that at least one of the hole injection/transportcompounds is a triarylamine-based compound.

(26) The organic electroluminescent device as set forth above in any oneof (1) to (21), wherein at least one of the electron injection/transportcompounds contained in the luminescent layer is a hydrocarbon-basedaromatic compound, and that at least one of the hole injection/transportcompounds is a pyrrole compound.

(27) The organic electroluminescent device as set forth above in any oneof (1) to (26), wherein the luminescent layer has at least one stackedlayer structure of an electron injection/transport compound and a holeinjection/transport compound.

(28) The organic electroluminescent device as set forth in any one of(1) to (26), wherein the luminescent layer contains a plurality ofdomain structures of an electron injection/transport compound and a holeinjection/transport compound.

The invention is concerned with an organic electroluminescent devicecomprising a pair of electrode and at least one organic layer includinga luminescent layer therebetween, wherein the luminescent layer containsat least one electron injection/transport compound, at least one holeinjection/transport compound, and at least one green or bluephosphorescent compound; and the electron injection/transport compoundand the hole injection/transport compound each has a minimum tripletexciton energy value (T₁ value) is equal to or more than that of thegreen or blue phosphorescent compound.

The luminescent layer contains at least three kinds of an electroninjection/transport compound, a hole injection/transport compound, and agreen or blue phosphorescent compound. The respective compounds shouldnot be identical with each other (for example, the luminescent layershould not be constituted of only two kinds of compounds). However, forexample, these compounds may be a polymer copolymer or oligomercomprising a skeleton (compound) having the respective function as amonomer unit. For example the luminescent layer may be constituted of acopolymer of a monomer unit functioning to inject/transport electronsand a monomer unit functioning to inject/transport holes and a compoundof emitting phosphorescence.

The content of each of the electron injection/transport compound, thehole injection/transport compound, and the green or blue phosphorescentcompound in the luminescent layer is not particularly limited, but it ispreferable that at least one of the electron injection/transportcompound and the hole injection/transport compound is the majorcomponent, whereas the green or blue phosphorescent compound is thesubsidiary component.

In the EL device of the invention, it is preferable to use a layercontaining a compound having an ionization potential of from 5.9 eV ormore (more preferably 6.0 eV or more), and more preferably an electrontransport layer having an ionization potential of 5.9 eV or more,between the cathode and the luminescent layer.

The invention is concerned with an organic luminescent device comprisinga pair of electrode and at least one organic layer including aluminescent layer therebetween. The organic layer is preferably anorganic layer including at least two layers of a luminescent layer andan electron injection/transport layer (the electron injection/transportlayer being aligned in the cathode side), and more preferably an organiclayer including at least three layers of a hole transport layer, aluminescent layer, and an electron transport layer, the electrontransport layer having an Ip value of 5.9 eV. It is further preferablethat the electron transport layer contains a compound represented by theformula (2).

(Electron Injection/Transport Compound)

An electron injection/transport compound contained in the luminescentlayer implies a compound which plays the role of injecting andtransporting electron in the luminescent layer. When such a compound isincorporated in the luminescent layer, the injection or transport ofelectron is promoted in some cases.

There are cases where a certain compound functions as an electroninjection/transport compound or as a hole injection/transport compoundin the luminescent layer depending on the mode in which the compound isused. For example, a hydrocarbon-based aromatic compound functions as ahole injection/transport compound when used in conjunction with acompound with a high electron injection/transport capability(exemplified by a nitrogen-containing heterocyclic compound, a metalcomplex, etc.), and functions as an electron injection/transportcompound when used in conjunction with a compound with a high holeinjection/transport capability (exemplified by a triarylamine compound,etc.).

The electron injection/transport compound preferably has an electronaffinity (Ea value) of from 2.0 eV to 3.5 eV, more preferably from 2.3eV to 3.4 eV, and further preferably from 2.5 eV to 3.3 eV.

The content of the electron injection/transport compound in theluminescent layer is preferable from 5% by weight to 90% by weight, morepreferably from 10% by weight to 85% by weight, further preferably from10% by weight to 80% by weight, and especially preferably from 10% byweight to 75% by weight.

Preferred examples of the electron injection/transport compound includemetal complexes (such as aluminum complexes and zinc complexes eachcomprising 2-hydroxyphenylbenzoimidazole ligand, provided that complexescomprising an 8-hydroxyquinolinol derivative (such as2-methyl-8-hydroxyquinolinol) as a ligand thereof are not preferable),nitrogen-containing heterocyclic compounds (such as azole derivatives,pyridine derivatives, and triazine derivatives), organosilicon compounds(such as silole derivatives, aryl silane derivatives), and aromatichydrocarbon compound (such as benzene, anthracene, pyrene) Of thesecompounds, heterocyclic compounds containing at least two nitrogen atomsand metal complexes are more preferable; heterocyclic compoundscontaining at least two nitrogen atoms are further preferable; andcompounds represented by the formula (2) are preferable as heterocycliccompounds containing at least two nitrogen atoms. Also, compoundsrepresented by the formulae (A-III), (A-IV), (A-V), (A), (A-a), (A-b),(A-c), (B-II), (B-III), (B-IV), (B-V), (B-VI), (B-VII), (B-VIII), and(B-IX) as described in JP-A-2002-100476 and compounds represented by theformulae (1) to (4) as described in JP-A-2000-302754 can be suitablyused (preferred ranges thereof are described in JP-A-2002-100476 andJP-A-2000-302754).

The formula (2) will be described below. R²¹ represents a hydrogen atomor a substituent. As the substituent on R²¹, the after-mentioned groupsdescribed for R¹¹ are enumerated. R²¹ is preferably an alkyl group, anaryl group, or a heteroaryl group; more preferably an aryl group or aheteroaryl group; and further preferably an aryl group and anitrogen-containing heteroaryl group.

X²¹, X²², X²³, and X²⁴ each represents a nitrogen atom or a substitutedor unsubstituted carbon atom. At least one of X²¹, X²², X²³, and X²⁴ isa nitrogen atom. As the substituent on the carbon atom, theafter-mentioned groups described for R¹² are enumerated. Above all, analkyl group, an aryl group, and a heteroaryl group are preferable.

It is preferable that X²¹ is a substituted or unsubstituted carbon atom,X² is a nitrogen atom, and X²³ and X²⁴ are each a substituted carbonatom. Also, it is preferable that the substituents on X²³ and X²⁴ arebonded to each other to form an aromatic ring.

A preferred embodiment of the compound represented by the formula (2) isa compound represented by the formula (4) or formula (5); and a morepreferred embodiment of the compound represented by the formula (2) is acompound represented by the formula (4).

The formula (4) will be described below. R⁴¹, R⁴², and R⁴³ eachrepresents a hydrogen atom or a substituent. As the substituent, forexample, the after-mentioned groups described for R¹² are enumerated.

R⁴¹ is preferably an alkyl group, an aryl group, or a heteroaryl group;more preferably an alkyl group or an aryl group; and further preferablyan alkyl group.

R⁴² and R⁴³ are each preferably an alkyl group, an aryl group, aheteroaryl group, or a group capable of forming an aromatic ring uponbonding to each other; and more preferably a group capable of forming anaromatic ring upon bonding to each other.

L⁴¹ represents a connecting group. The connecting group may be a polymermain chain of polyalkylene, polyester, etc. (for example, it may form apolyvinylimidazole derivative). L⁴¹ is preferably an aryl connectinggroup, a heteroaryl connecting group, an alkyl connecting group, or analkylene polymer main chain; more preferably an aryl connecting group ora heteroaryl connecting group; and further preferably anitrogen-containing heteroaryl connecting group.

n⁴¹ represents an integer of 2 or more. In the case where L⁴¹ is not apolymer main chain, n⁴¹ is preferably from 2 to 6, and more preferablyfrom 3 to 4. In the case where L⁴¹ is a polymer main chain, n⁴¹ is avalue corresponding to the repeating unit of the polymer main chain (forexample, in the case of a 100mer of vinylbenzimidazole, n⁴¹ is 100).

L⁴² and n⁴² are synonymous with the after-mentioned L³² and n³²,respectively, and preferred ranges thereof are also the same.

The formula (5) will be described below. R⁵² and R⁵³ each represents ahydrogen atom or a substituent. As the substituent, for example, theafter-mentioned groups described for R¹² are enumerated.

R⁵² and R⁵³ are each preferably an alkyl group, an aryl group, aheteroaryl group, or a group capable of forming an aromatic ring uponbonding to each other; more preferably a group capable of forming anaromatic ring upon bonding to each other; and further preferably a groupcapable of forming a nitrogen-containing aromatic ring upon bonding toeach other.

R⁵⁴ represents a hydrogen atom or a substituent. As the substituent, forexample, the after-mentioned groups described for R¹¹ are enumerated.R⁵⁴ is preferably an alkyl group, an aryl group, or a heteroaryl group;more preferably an aryl group or a heteroaryl group; and furtherpreferably an aryl group.

L⁵¹, L⁵², n⁵¹, and n⁵² are synonymous with the foregoing L⁴¹, L⁴², n⁴¹,and n⁴², respectively, and preferred ranges thereof are also the same.

As the electron injection/transport compound of the present invention, anitrogen-containing six-membered cyclic compound is also preferred. Suchnitrogen-containing six-membered cyclic compounds, which have no speciallimitation, include, for example, pyridine, pyrazine, pyrimidine,pyridazine, triazine, and condensed ring compounds comprising theserings (quinoline, quinoxaline, etc.). And nitrogen-containingsix-membered monocyclic compounds are more preferred.

As the nitrogen-containing 6-membered cyclic compound, those representedby formulae (8) to (11) are preferred, those represented by formulae(8), (10) and (11) are more preferred, those represented by formulae (8)and (11) are still more preferred, and those represented by formula (11)are particularly preferred.

Formulae (8) to (11) will be explained. R⁸¹ to R⁸⁵, R⁹¹ to R⁹⁴, R¹⁰¹ toR¹⁰⁴ and R¹¹¹ to R¹¹³ each represent a hydrogen atom, or a substituent.And as such a substituent, those explained as R¹¹ to be shown later arementioned. The substituents may be bonded with each other to form acondensed ring structure (exemplified by benzo-condensed ring,pyridine-condensed ring, etc.).

R⁸¹ to R⁸⁵, R⁹¹ to R⁹⁴, R¹⁰¹ to R¹⁰⁴ and R¹¹¹ to R¹¹³ each preferablyrepresent a hydrogen atom, an alkyl group, an aryl group, a heteroarylgroup, a fluorine atom, and an amino group. But among them, a hydrogenatom, an aryl group, a heteroaryl group are more preferred.

Further, as the electron injection/transport compound of the invention,nitrogen-containing 5- or 6-membered cyclic compounds represented byformulae (I) and (II) set forth in JP-A-2002-356489, and represented byformula (I) set forth in JP-A-2002-338579 are preferred. The preferablerange of these compounds, and compound examples are described inJP-A-2002-356489 and JP-A-2002-338579.

(Hole Injection/Transport Compound)

A hole injection/transport compound contained in the luminescent layerimplies a compound which plays the role of injecting and transportinghole in the luminescent layer. When such a compound is incorporated inthe luminescent layer, the injection or transport of hole is promoted insome cases.

There are cases where a certain compound functions as a holeinjection/transport compound or as an electron injection/transportcompound in the luminescent layer depending on the mode in which thecompound is used. For example, a hydrocarbon-based aromatic compoundfunctions as a hole injection/transport compound when used inconjunction with a compound with a high electron injection/transportcapability (exemplified by a nitrogen-containing heterocyclic compound,a metal complex, etc.), and functions as an electron injection/transportcompound when used in conjunction with a compound with a high holeinjection/transport capability (exemplified by a triarylamine compound,etc.).

The hole injection/transport compound preferably has an Ip value(ionization potential) of from 5.6 eV to 6.1 eV, more preferably from5.7 eV to 6.1 eV, further preferably from 5.7 eV to 6.0 eV, andespecially preferably from 5.8 eV to 6.0 eV.

The concentration of the hole injection/transport compound in theluminescent layer is preferably from 10% by weight to 95% by weight,more preferably from 15% by weight to 90% by weight, further preferablyfrom 30% by weight to 85% by weight, and especially preferably from 30%by weight to 80% by weight.

Preferred examples of the hole injection/transport compound includehydrocarbon based aromatic derivatives (such as benzene derivatives,anthracene derivatives, and pyrene derivatives), pyrrole derivatives(such as pyrrole derivatives, indole derivatives, and carbazolederivatives), and azepine derivatives (such as tribenzoazepinederivatives). Of these compounds, pyrrole derivatives are morepreferable, and compounds represented by the formula (1) are furtherpreferable.

The formula (1) will be described below. R¹¹ to R¹⁵ each represents ahydrogen atom or a substituent, and the substituents may be bonded toeach other to form a ring structure (such as a benzene ring and apyridine ring). Examples of the substituent represented by R¹¹ includean alkyl group (preferably ones having from 1 to 30 carbon atoms, morepreferably from 1 to 20 carbon atoms, and especially preferably from 1to 10 carbon atoms, such as a methyl group, an ethyl group, an isopropylgroup, a t-butyl group, an n-octyl group, an n-decyl group, ann-hexadecyl group, a cyclopropyl group, a cyclopentyl group, and acyclohexyl group), an alkenyl group (preferably ones having from 2 to 30carbon atoms, more preferably from 2 to 20 carbon atoms, and especiallypreferably from 2 to 10 carbon atoms, such as a vinyl group, an allylgroup, a 2-butenyl group, and a 3-pentenyl group), an alkynyl group(preferably ones having from 2 to 30 carbon atoms, more preferably from2 to 20 carbon atoms, and especially preferably from 2 to 10 carbonatoms, such as a propargyl group and a 3-pentynyl group), an aryl group(preferably ones having from 6 to 30 carbon atoms, more preferably from6 to 20 carbon atoms, and especially preferably from 6 to 12 carbonatoms, such as a phenyl group, a p-methylphenyl group, a naphthyl group,and an anthranyl group), an acyl group (preferably ones having from 1 to30 carbon atoms, more preferably from 1 to 20 carbon atoms, andespecially preferably from 1 to 12 carbon atoms, such as an acetylgroup, a benzoyl group, a formyl group, and a pivaloyl group), asulfonyl group (preferably ones having from 1 to 30 carbon atoms, morepreferably from 1 to 20 carbon atoms, and especially preferably from 0.1to 12 carbon atoms, such as a mesyl group and a tosyl group), aheterocyclic group (preferably ones having from 1 to 30 carbon atoms andmore preferably from 1 to 12 carbon atoms, in which examples of thehetero atom include a nitrogen atom, an oxygen atom, and a sulfur atom,such as an imidazolyl group, a pyridyl group, a quinolyl group, a furylgroup, a thienyl group, a piperidyl group, a morpholino group, abenzoxazolyl group, a benzimidazolyl group, a benzthiazolyl group, acarbazolyl group, and an azepinyl group), and a silyl group (preferablyones having from 3 to 40 carbon atoms, more preferably from 3 to 30carbon atoms, and especially preferably from 3 to 24 carbon atoms, suchas a trimethylsilyl group and a triphenylsilyl group). Thesesubstituents may further be substituted. Examples of the substituentrepresented by R¹² to R¹⁵ include ones of the following substituentgroup A.

(Substituent Group A)

Examples include an alkyl group (preferably ones having from 1 to 30carbon atoms, more preferably from 1 to 20 carbon atoms, and especiallypreferably from 1 to 10 carbon atoms, such as a methyl group, an ethylgroup, an isopropyl group, a t-butyl group, an n-octyl group, an n-decylgroup, an n-hexadecyl group, a cyclopropyl group, a cyclopentyl group,and a cyclohexyl group), an alkenyl group (preferably ones having from 2to 30 carbon atoms, more preferably from 2 to 20 carbon atoms, andespecially preferably from 2 to 10 carbon atoms, such as a vinyl group,an allyl group, a 2-butenyl group, and a 3-pentenyl group), an alkynylgroup (preferably ones having from 2 to 30 carbon atoms, more preferablyfrom 2 to 20 carbon atoms, and especially preferably from 2 to 10 carbonatoms, such as a propargyl group and a 3-pentynyl group), an aryl group(preferably ones having from 6 to 30 carbon atoms, more preferably from6 to 20 carbon atoms, and especially preferably from 6 to 12 carbonatoms, such as a phenyl group, a p-methylphenyl group, a naphthyl group,and an anthranyl group), an amino group (preferably ones having from 0to 30 carbon atoms, more preferably from 0 to 20 carbon atoms, andespecially preferably from 0 to 10 carbon atoms, such as an amino group,a methylamino group, a dimethylamino group, a diethylamino group, adibenzylamino group, a diphenylamino group, and a ditolylamino group),an alkoxy group (preferably ones having from 1 to 30 carbon atoms, morepreferably from 1 to 20 carbon atoms, and especially preferably from 1to 10 carbon atoms, such as a methoxy group, an ethoxy group, a butoxygroup, and a 2-ethylhexyloxy group), an aryloxy group (preferably oneshaving from 6 to 30 carbon atoms, more preferably from 6 to 20 carbonatoms, and especially preferably from 6 to 12 carbon atoms, such as aphenyloxy group, a 1-naphthyloxy group, and a 2-naphthyloxy group), aheterocyclic oxy group (preferably ones having from 1 to 30 carbonatoms, more preferably from 1 to 20 carbon atoms, and especiallypreferably from 1 to 12 carbon atoms, such as a pyridyloxy group, apyrazyloxy group, a pyrimidyloxy group, and a quinolyloxy group), anacyl group (preferably ones having from 1 to 30 carbon atoms, morepreferably from 1 to 20 carbon atoms, and especially preferably from 1to 12 carbon atoms, such as an acetyl group, a benzoyl group, a formylgroup, and a pivaloyl group),

an alkoxycarbonyl group (preferably ones having from 2 to 30 carbonatoms, more preferably from 2 to 20 carbon atoms, and especiallypreferably from 2 to 12 carbon atoms, such as a methoxycarbonyl groupand an ethoxycarbonyl group), an aryloxycarbonyl group (preferably oneshaving from 7 to 30 carbon atoms, more preferably from 7 to 20 carbonatoms, and especially preferably from 7 to 12 carbon atoms, such as aphenyloxycarbonyl group), an acyloxy group (preferably ones having from2 to 30 carbon atoms, more preferably from 2 to 20 carbon atoms, andespecially preferably from 2 to 10 carbon atoms, such as an acetoxygroup and a benzoyloxy group), an acylamino group (preferably oneshaving from 2 to 30 carbon atoms, more preferably from 2 to 20 carbonatoms, and especially preferably from 2 to 10 carbon atoms, such as anacetylamino group and a benzoylamino group), an alkoxycarbonylaminogroup (preferably ones having from 2 to 30 carbon atoms, more preferablyfrom 2 to 20 carbon atoms, and especially preferably 2 to 12 carbonatoms, such as a methoxycarbonylamino group), an aryloxycarbonylaminogroup (preferably ones having from 7 to 30 carbon atoms, more preferablyfrom 7 to 20 carbon atoms, and especially preferably from 7 to 12 carbonatoms, such as a phenyloxycarbonylamino group), a sulfonylamino group(preferably ones having from 1 to 30 carbon atoms, more preferably from1 to 20 carbon atoms, and especially preferably from 1 to 12 carbonatoms, such as a methanesulfonylamino group and a benzenesulfonylaminogroup), a sulfamoyl group (preferably ones having from 0 to 30 carbonatoms, more preferably from 0 to 20 carbon atoms, and especiallypreferably from 0 to 12 carbon atoms, such as a sulfamoyl group, amethylsulfamoyl group, a dimethylsulfamoyl group, and a phenylsulfamoylgroup), a carbamoyl group (preferably ones having from 1 to 30 carbonatoms, more preferably from 1 to 20 carbon atoms, and especiallypreferably from 1 to 12 carbon atoms, such as a carbamoyl group, amethylcarbamoyl group, a diethylcarbamoyl group, and a phenylcarbamoylgroup), an alkylthio group (preferably ones having from 1 to 30 carbonatoms, more preferably from 1 to 20 carbon atoms, and especiallypreferably from 1 to 12 carbon atoms, such as a methylthio group and anethylthio group),

an arylthio group (preferably ones having from 6 to 30 carbon atoms,more preferably from 6 to 20 carbon atoms, and especially preferablyfrom 6 to 12 carbon atoms, such as a phenylthio group), a heterocyclicthio group (preferably ones having from 1 to 30 carbon atoms, morepreferably from 1 to 20 carbon atoms, and especially preferably from 1to 12 carbon atoms, such as a pyridylthio group, a 2-benzimidazolylthiogroup, a 2-benzoxazolylthio group, and a 2-benzthiazolylthio group), asulfonyl group (preferably ones having from 1 to 30 carbon atoms, morepreferably from 1 to 20 carbon atoms, and especially preferably from 1to 12 carbon atoms, such as a mesyl group and tosyl group), a sulfinylgroup (preferably ones having from 1 to 30 carbon atoms, more preferablyfrom 1 to 20 carbon atoms, and especially preferably from 1 to 12 carbonatoms, such a methanesulfinyl group and a benzenesulfinyl group), aureido group (preferably ones having from 1 to 30 carbon atoms, morepreferably from 1 to 20 carbon atoms, and especially preferably from 1to 12 carbon atoms, such as a ureido group, a methylureido group, and aphenylureido group), a phosphoric acid amide group (preferably oneshaving from 1 to 30 carbon atoms, more preferably from 1 to 20 carbonatoms, and especially preferably from 1 to 12 carbon atoms, such as adiethylphosphoric acid amide group and a phenylphosphoric acid amidegroup), a hydroxyl group, a mercapto group, a halogen atom (such as afluorine atom, a chlorine atom, a bromine atom, and an iodine atom), acayno group, a sulfo group, a carboxyl group, a nitro group, ahydroxamic acid group, a sulfino group, a hydrazino group, an iminogroup, a heterocyclic group (preferably ones having from 1 to 30 carbonatoms and more preferably from 1 to 12 carbon atoms, in which examplesof the hetero atom include a nitrogen atom, an oxygen atom, and a sulfuratom, such as an imidazolyl group, a pyridyl group, a quinolyl group, afuryl group, a thienyl group, a piperidyl group, a morpholino group, abenzoxazolyl group, a benzimidazolyl group, a benzthiazolyl group, acarbazolyl group, and an azepinyl group), a silyl group (preferably oneshaving from 3 to 40 carbon atoms, more preferably from 3 to 30 carbonatoms, and especially preferably from 3 to 24 carbon atoms, such as atrimethylsilyl group and a triphenylsilyl group), and a silyloxy group(preferably ones having from 3 to 40 carbon atoms, more preferably from3 to 30 carbon atoms, and especially preferably from 3 to 24 carbonatoms, such as a trimethylsiloxy group and a triphenylsilyloxy group).These substituents may further be substituted.

R¹¹ is preferably an alkyl group, an aryl group, or a heteroaryl group,and more preferably an alkyl group or an aryl group.

R¹² to R¹⁵ are each preferably a hydrogen atom, an alkyl group, or agroup capable of forming a benzene ring upon bonding to each other. Thecompound represented by the formula (1) is preferably a substituted orunsubstituted indole or a substituted or unsubstituted carbazole.

The compound represented by the formula (1) is preferably a compoundrepresented by the formula (3).

The formula (3) will be described below. R³² to R³⁵ are synonymous withthe foregoing R¹² to R¹⁵, respectively, and preferred ranges thereof arealso the same.

L³¹ represents a connecting group. The connecting group may be a polymermain chain of polyalkylene, polyester, etc. (for example, it may form apolyvinylpyrrole derivative). L³¹ is preferably an aryl connectinggroup, a heteroaryl connecting group, an alkyl connecting group, anamino connecting group (n³² preferably represents an integer of 1 ormore), or an alkylene polymer main chain, and more preferably an arylconnecting group, an amino connecting group (n³² preferably representsan integer of 1 or more) or an alkylene main chain.

L³² represents a di- or more valent connecting group. L³² is preferablyan alkylene group, an arylene group, a heteroarylene group, an oxygenconnecting group, a carbonyl connecting group, or an amino connectinggroup, and more preferably an alkylene group or an arylene group.

n³¹ represents an integer of 2 or more. In the case where n³¹ is plural,plural nitrogen-containing heterocyclic groups may be the same ordifferent. In the case where L³² is not a polymer main chain, n³¹ ispreferably from 2 to 6, and more preferably from 3 to 4. In the casewhere L³¹ is a polymer main chain, n³¹ is a value corresponding to therepeating unit of the polymer main chain (for example, in the case of a100mer of vinylcarbazole, n³¹ is 100).

n³² represents an integer of from 0 to 6, preferably from 0 to 3, andmore preferably 0 or 1. In the case where n³² is plural, plural L³²'smay be the same or different.

The electron injection/transport compound and the holeinjection/transport compound each preferably has a glass transitionpoint of 100° C. to 500° C., more preferably from 110° C. to 300° C.,and further preferably from 120° C. to 250° C.

As the triarylamine derivatives used as a hole injection/transportcomound, those represented by formula (6) are preferred.

Formula (6) will be explained. R⁶¹, R⁶² and R⁶³ each represent asubstituent. As the substituent, the groups described as theaforementioned R¹¹ are mentioned. Two substituents may be bonded to eachother to form a cyclic structure. R⁶¹, R⁶² and R⁶³ each represent analkyl group, an aryl group, a heteroaryl group, an alkenyl group, analkoxy group, and an amino group. Among them, an alkyl group, an arylgroup, and a heteroaryl group are more preferred, and an aryl group (forexample, phenyl group, naphthyl group, phenanthryl group, triphenylenylgroup, futraphenylenyl group, etc.), a heteroaryl group (for example,pyridyl group, pyrazyl group, pyrimidyl group, triazyl group,benzoimidazolyl group, benzoxazolyl group, oxadiazolyl group, etc.) arestill more preferred.

n⁶¹, n⁶² and n⁶³ each represent an integer of from 0 to 5 whereby 1 to 5are preferred and 1 to 3 is more preferred. In cases where n⁶¹, n⁶² andn⁶³ are 2 to 5, plural R⁶¹, R⁶² and R⁶³ may be the same or differentfrom each other.

As the triarylamine derivative represented by formula (6), a monoaminederivative (which has only one triarylamine structure in the molecule)is preferred.

As the hydrocarbon-based aromatic compound used as the holeinjection/transport compound, those compounds represented by formula (7)are preferred.

Explanation will be given on Formulae (7).

R⁷⁰ and R⁷¹ each represent an alkyl group, an aryl group, and onecapable of forming a hydrocarbon ring (such as, for example, naphthalenering, phenanthrene ring, triphenylene ring, tetraphenylene ring, etc.)upon bonding to each other. These substituents may further have asubstituent (such as those explained as the foregoing R¹¹).

Each of R⁷⁰ and R⁷¹ is preferably a hydrogen atom, an aryl group or agroup capable of forming a hydrocarbon ring upon bonding to each other.In particular, it is preferred that at least two of R⁷⁰ and R⁷¹ are arylgroups, or that at least one pair of R⁷⁰ and R⁷¹ is a group capable offorming a hydrocarbon ring upon bonding to each other.

(Green or Blue Phosphorescent Compound)

The green or blue phosphorescent compound (sometimes referred to simplyas “phosphorescent compound” in this specification) to be used in theinvention means a compound that when contained in the luminescent layerof the EL device, emits green or blue phosphorescence by energy transferfrom the electron injection/transport compound and/or the holeinjection/transport compound by application of an electric field betweena pair of electrodes. Though the green or blue phosphorescent compoundis not particularly limited, ones capable of simultaneously emittingfluorescence may be employed. Compounds that when contained in theluminescent layer of the EL device, have a phosphorescent intensity of 2times or more as compared with the fluorescent intensity to be emittedfrom the luminescent layer of the organic EL device are preferable. Ofthese compounds, those having a phosphorescent intensity of 10 times ormore are more preferable, and those having a phosphorescent intensity of100 times or more are further preferable.

Emission of green or blue phosphorescence means that the peak wavelengthof the phosphorescent emission light lies between 400 nm and 590 nm,preferably between 410 nm and 570 nm, more preferably between 410 nm and560 nm, and still more preferably between 420 nm and 550 nm.

In the invention, as the phosphorescent compound, transition metalcomplexes capable of emitting fluorescence are preferable; iridiumcomplexes, platinum complexes, rhenium complexes, ruthenium complexes,palladium complexes, rhodium complexes, and rare earth complexes aremore preferable; iridium complexes and platinum complexes are furtherpreferable; orthocarbometalated iridium complexes are especiallypreferable; and orthocarbometalated iridium complexes having adifluorophenylpyridine ligand are most preferable. Also,orthocarbometalated iridium complexes having a difluorophenylpyridineligand described in JP-A-2002-235076, JP-A-2002-170684, and JapanesePatent Application Nos. 2001-239281 and 2001-248165 are preferable.

Furthermore, such phosphorescent compounds emitting blue to green lightcan also be used which are set forth in various patent literaturesincluding U.S. Pat. No. 6,303,238 B1, U.S. Pat. No. 6,097,147, WO00/57676, WO 00/70655, WO 01/08230, WO 01/39234 A2, WO 01/41512 A1, WO02/02714 A2, WO 02/15645 A1, JP-A-2001-247859, Japanese PatentApplication No. 2000-33561, Japanese Patent Application No. 2001-189539,Japanese Patent Application No. 2001-248165, Japanese Patent ApplicationNo. 2001-33684, Japanese Patent Application No. 2001-239281, JapanesePatent Application No. 2001-219909, EP 1211257, JP-A-2002-226495,JP-A-2002-234894, JP-A-2001-247859, JP-A-2001-298470, JP-A-2002-173674,JP-A-2002-203678, JP-A-2002-203679, etc.

In the invention, the concentration of the phosphorescent compound inthe luminescent layer is preferably from 1% by weight to 30% by weight,more preferably from 2% by weight to 20% by weight, and furtherpreferably from 3% by weight to 15% by weight.

The phosphorescence obtained from the phosphorescent compound of the ELdevice of the invention preferably has, as regards the blueelectroluminescent device, a % max (emission maximum wavelength) of from350 nm to 500 nm, more preferably from 400 nm to 500 nm, and furtherpreferably from 420 nm to 500 nm.

In the EL device of the invention, as regards the blueelectroluminescent device, it is preferable that the electroninjection/transport compound, the hole injection/transport compound andthe phosphorescent compound of the invention each has a T₁ value of 62kcal/mole or more, and the phosphorescence obtained from thephosphorescent compound of the invention has a λmax (emission maximumwavelength) of from 350 nm to 500 nm; it is more preferable that theelectron injection/transport compound, the hole injection/transportcompound and the phosphorescent compound of the invention each has a T₁value of 63 kcal/mole or more, and the phosphorescence obtained from thephosphorescent compound of the invention has a λmax (emission maximumwavelength) of from 350 nm to 490 nm; it is further preferable that theelectron injection/transport compound, the hole injection/transportcompound and the phosphorescent compound of the invention each has a T₁value of 64 kcal/mole or more, and the phosphorescence obtained from thephosphorescent compound of the invention has a λmax (emission maximumwavelength) of from 350 nm to 480 nm; and it is especially preferablethat the electron injection/transport compound, the holeinjection/transport compound and the phosphorescent compound of theinvention each has a T₁ value of 65 kcal/mole or more, and thephosphorescence obtained from the phosphorescent compound of theinvention has a λmax (emission maximum wavelength) of from 350 nm to 475nm. (for reference, 1 kcal/mole can be converted to 4.184 kJ/mol.)

As regards the green electroluminescent device among the EL device ofthe invention, it is preferable that the electron injection/transportcompound, the hole injection/transport compound and the phosphorescentcompound each have a T₁ value of 53 kcal/mole or more, and thephosphorescence obtained from the phosphorescent compound of theinvention has a λmax (maximum emission wavelength) of from 590 nm orshorter; it is more preferable that the electron injection/transportcompound, the hole injection/transport compound and the phosphorescentcompound each have a T₁ value of 55 kcal/mole or more, and thephosphorescence obtained from the phosphorescent compound has a λmax(maximum emission wavelength) of 570 nm or shorter; it is still morepreferable that the electron injection/transport compound, the holeinjection/transport compound and the phosphorescent compound each have aT₁ value of 56 kcal/mole or more, and the phosphorescence obtained fromthe phosphorescent compound of the invention has a λmax (emissionmaximum wavelength) of 560 nm or shorter; and it is especiallypreferable that the electron injection/transport compound, the holeinjection/transport compound and the phosphorescent compound each have aT₁ value of 57 kcal/mole or more, and the phosphorescence obtained fromthe phosphorescent compound of the invention has a % max (emissionmaximum wavelength) of 550 nm or shorter.

The phosphorescent life (at room temperature) of the phosphorescentcompound of the invention is not specifically limited, but is preferably1 ms or less, more preferably 100 μs or less, and still more preferably10 μs or less.

The compounds represented by the formulae (1) to (5) of the inventionmay be each a low-molecular compound or may be an oligomer compound or apolymer compound (the weight average molecular weight (as reduced intopolystyrene) is preferably 1,000 to 5,000,000, more preferably from2,000 to 1,000,000, and further preferably from 3,000 to 100,000). Inthe case of the polymer compound, each of the structures of the formulae(1) to (5) may be contained in the polymer main chain or may becontained in the polymer side chain. Also, in the case of the polymercompound, the polymer compound may be a homopolymer compound or acopolymer.

Next, specific examples of the compounds of the invention will be givenbelow, but it should not be construed that the invention is limitedthereto.

(EL Device of the Invention)

The EL device of the invention will be described below. The EL device ofthe invention is not particularly limited with respect to the system,driving method, and utilization embodiment.

The formation method of the organic compound layer of the EL device ofthe invention is not particularly limited. Examples include a resistanceheating vapor deposition method, an electron beam method, a sputteringmethod, a molecular lamination method, a coating method (such as spraycoating, dip coating, impregnation, roll coating, gravure coating,reverse coating, roll brush coating, air knife coating, curtain coating,spin coating, flow coating, bar coating, micro-gravure coating, airdoctor coating, blade coating, squeeze coating, transfer roll coating,kiss coating, cast coating, extrusion coating, wire bar coating, andscreen coating), an inkjet method, a printing method, and a transfermethod. Above all, taking into consideration characteristics andmanufacture, a resistance heating vapor deposition method, a coatingmethod, and a transfer method are preferable.

The EL device of the invention is a device in which a luminescent layeror plural organic compound films containing a luminescent layer areformed between a pair of electrodes of an anode and a cathode. The ELdevice of the invention may have a hole injection layer, a holetransport layer, an electron injection layer, an electron transportlayer, and a protective layer in addition to the luminescent layer.Also, each of these layers may have other function at the same time. Informing the respective layers, various materials can be used.

The EL device of the invention can improve light extraction efficiencywith various, publicly known measures. It is possible to enhanceexternal quantum efficiency by improving light extraction efficiency,for example, by the following measures; processing the surfaceconfiguration of the support (for example, formation of fineconcavo-convex patterns), control of the refractive indices of thesupport, the ITO layer and the organic layers, regulation of thethicknesses of the support, the ITO layer and the organic layers, etc.

The EL device of the invention may be of so-called top emission type inwhich the emitted light is taken out from the cathode side.

The support material used for the EL device of the invention are notspecifically restricted, and include inorganic materials such aszirconia-stabilized yttrium, glass, etc., macro-molecular weightmaterials such as polyesters exemplified by poly (ethyleneterephthalate), poly(butylene terephthalate), poly(ethylenenaphthalate), etc., polyethylene, polycarbonate, polyether sulfone,polyallylate, allyl diglycol carbonate, polyimide, polycyclo-olefinnorbornene resin, poly(chlorotrifluoroethylene), teflon,polytetrafluoroethylene-polyethylene copolymer, etc.

The organic electroluminescent device of the invention may use a blueelectroluminescent device based on singlet exciton in combination.

The luminescent layer of the organic electroluminescent device inaccordance with the invention may include at least one stacked layerstructure of an electron transport compound and a hole transportcompound. Among the luminescent layers, there may be present anothertype of layer structure. The number of the stacked layers may bepreferably from 2 to 50, more preferably from 4 to 30, and still morepreferably from 6 to 20.

The thickness of each layer constituting the stacked layer structure isnot specifically limited, and is preferably from 0.2 nm to 20 nm, morepreferably from 0.4 nm to 15 nm, still more preferably from 0.5 nm to 10nm, and especially preferably from 1 nm to 5 nm.

In the luminescent layer in the organic electroluminescent device of theinvention, each of an electron transport compound and a hole transportcompound may have a plurality of domain structures. The luminescentlayer may further contain another type of domain structure. The size ofsuch individual domains is preferably from 0.2 nm to 10 nm, morepreferably from 0.3 nm to 5 nm, still more preferably from 0.5 nm to 3nm, and especially preferably from 0.7 nm to 2 nm.

The anode feeds holes into the hole injection layer, the hole transportlayer, the luminescent layer, etc. As the anode, metals, alloys, metaloxides, electroconductive compounds, or mixtures thereof can be used. Ofthese, materials having a work function of 4 eV or more are preferable.Specific examples include conductive metal oxides such as tin oxide,zinc oxide, indium oxide, and indium-tin oxide (ITO); metals such asgold, silver, chromium, and nickel; mixtures or laminates of theforegoing metals and conductive metal oxides; inorganic conductivesubstances such as copper iodide and copper sulfide; organic conductivematerials such as polyaniline, polythiophene, and polypyrrole; andmixtures or laminates thereof with ITO. Of these, conductive metaloxides are preferable, and ITO is especially preferable from theviewpoints of productivity, high conductivity, and transparency. Thoughthe film thickness of the anode can be properly chosen according to thematerial, in general, it is preferably in the range of from 10 nm to 5μm, more preferably from 50 nm to 1 μm, and further preferably from 100nm to 500 nm.

As the anode, a layer formed on a substrate such as a soda lime glass,an alkali-free glass, and a transparent resin is used. In the case ofusing a glass, with respect to the material quality, it is preferable touse an alkali-free glass for the sake of reducing ions eluted from theglass. Also, in the case of using a soda lime glass, it is preferable touse one on which a barrier coat such as silica is provided. Thethickness of the substrate is not particularly limited so far as it issufficient for keeping a mechanical strength. In the case of using aglass, in general, ones having a thickness of 0.2 mm or more, andpreferably 0.7 mm or more are used.

For preparation of the anode, various methods can be employed accordingto the material. For example, in the case of ITO, the film formation iscarried out by an electron beam method, a sputtering method, aresistance heating vapor deposition method, a chemical reaction method(such as a sol-gel method), coating of indium-tin oxide dispersion, etc.

In the anode, it is possible to lower the driving voltage of the deviceand enhance luminous efficiency by rinsing or other treatment. Forexample, in the case of ITO, UV-ozone treatment, plasma treatment, etc.are effective.

The cathode feeds electrons into the electron injection layer, theelectron transport layer, the luminescent layer, etc. and is chosentaking into consideration adhesiveness to an adjacent layer to thecathode, such as the electron injection layer, the electron transportlayer, and the luminescent layer, ionization potential, stability, etc.As materials of the cathode, metals, alloys, metal halides, metaloxides, electroconductive compounds, or mixtures thereof can beemployed. Specific examples include alkali metals (such as Li, Na, andK) or fluorides thereof, alkaline earth metals (such as Mg and Ca) orfluorides thereof, gold, silver, lead, aluminum, a sodium-potassiumalloy or mixed metals thereof, a lithium-aluminum alloy or mixed metalsthereof, a magnesium-silver alloy or mixed metals thereof, and rareearth metals such as indium and ytterbium. Of these, materials having awork function of not more than 4 eV are preferable; and aluminum, alithium-aluminum alloy or mixed metals thereof, and a magnesium-silverally or mixed metals thereof are more preferable. The cathode can alsotake a laminate structure containing the foregoing compounds or mixturesin addition of the single layer structure of the foregoing compounds ormixtures. For example, a laminate structure such as aluminum/lithiumfluoride and aluminum/lithium oxide is preferable. Though the filmthickness of the cathode can be properly chosen according to thematerial, in general, it is preferably in the range of from 10 nm to 5μm, more preferably from 50 nm to 1 μm, and further preferably from 100nm to 1 μm.

For forming the cathode, an electron beam method, a sputtering method, aresistance heating vapor deposition method, a coating method, a transfermethod, etc. can be employed. A single metal can be vapor deposited, ortwo or more components can be vapor deposited at the same time. Further,it is possible to subject plural metals to vapor deposition at the sametime to form an alloy electrode. Also, an alloy having been prepared inadvance may be vapor deposited. It is preferable that the sheetresistance of the anode and cathode is low, and it is preferably lessthan several hundreds Ω/□ (Ω/square).

As the material of the luminescent layer, any materials capable offorming a layer having a function such that not only holes from theanode or the hole injection layer or hole transport layer can beinjected, but also electrons from the cathode or the electron injectionlayer or electron transport layer can be injected upon application of anelectric field, having a function to transfer the injected charges, orhaving a function capable of providing a field of recombination of holesand electrons to cause light emission can be employed. Examples ofmaterials other than the compounds of the invention include benzoxazole,benzoimidazole, benzothiazole, styrylbenzene, polyphenyl,diphenylbutadiene, tetraphenylbutadiene, naphthalimide, coumarin,perylene, perinone, oxadiazole, aldazine, pyrralizine, cyclopentadiene,bis-styrylanthracene, quinacridone, pyrropyridine, thiadiazolopyridine,cyclopentadiene, styrylamine, aromatic dimethylidene compounds, variousmetal complexes represented by 8-quinolinol metal complexes or rareearth complexes, polymer compounds (such as polythiophene,polyphenylene, and polyphenyelenevinylene), organic silanes, iridiumtris-phenylpyridine complexes, transition metal complexes capable ofemitting phosphorescence represented by platinum porphyrin complexes,and derivatives thereof. Though the film thickness of the luminescentlayer is not particularly limited, in general it is preferably in therange of from 1 nm to 5 μm, more preferably from 5 nm to 1 μm, andfurther preferably from 10 nm to 500 nm.

The formation method of the luminescent layer is not particularlylimited. Examples include a resistance heating vapor deposition method,an electron beam method, a sputtering method, a molecular laminationmethod, a coating method, an inkjet method, a printing method, an LBmethod, and a transfer method. Of these methods, a resistance heatingvapor deposition method and a coating method are preferable.

The luminescent layer may be a single layer or a plurality of layers,and the respective layers cause light emission at a luminescencedifferent from each other. For example, a white luminescence may becaused. A white luminescence may be emitted from the single luminescentlayer.

As materials of the hole injection layer and hole transport layer, anymaterials having any one of a function to inject holes from an anode, afunction to transport holes, or a function to obstruct electronsinjected from a cathode are employable. Specific examples includecarbazoles, triazoles, oxazoles, oxadiazoles, imidazoles,polyarylalkanes, pyrazoline, pyrazolone, phenylenediamine, arylamines,amino-substituted chalcone, styrylanthracene, fluorenones, hydrazones,stilbene, silazanes, aromatic tertiary amine compounds, styrylaminecompounds, aromatic dimethylidene based compounds, porphyrin basedcompounds, conductive high-molecular oligomers such as polysilane basedcompounds, poly-N-vinylcarbazole, aniline based copolymers, thiopheneoligomers, and polythiophenes, organic silanes, carbon films, compoundsof the inventions, and derivatives of the foregoing compounds. Thoughthe film thickness of the hole injection layer and hole transport layeris not particularly limited, in general, it is preferably in the rangeof from 1 nm to 5 μm, more preferably in the range of from 5 nm to 1 μm,and further preferably in the range of from 10 nm to 500 nm. Each of thehole injection layer and the hole transport layer may be of a singlelayer structure made of one or two or more kinds of the foregoingmaterials, or may be of a multilayered structure comprising a pluralityof layers of the same formulation or a different formation from eachother.

Examples of the formation method of the hole injection layer and thehole transport layer include a vacuum deposition method, an LB method, amethod of coating a solution or dispersion of the foregoing holeinjection/transport material in a solvent, an inkjet method, a printingmethod, and a transfer method. In the case of the coating method, thehole injection/transport material can be dissolved or dispersed togetherwith a resin component. Examples of the resin component includepolyvinyl chloride, polycarbonate, polystyrene, polymethyl methacrylate,polybutyl methacrylate, polyesters, polysulfone, polyphenylene oxide,polybutadiene, poly(N-vinylcarbazole), hydrocarbon resins, ketoneresins, phenoxy resins, polyamides, ethyl cellulose, polyvinyl acetate,ABS resins, polyurethanes, melamine resins, unsaturated polyesterresins, alkyd resins, epoxy resins, and silicone resins.

As materials of the electron injection layer and electron transportlayer, any materials having any one of a function to inject electronsfrom a cathode, a function to transport electrons, or a function toobstruct electrons injected from an anode are employable. Specificexamples include triazines, oxazoles, oxadiazoles, imidazoles,fluorenones, anthraquinodimethane, anthrone, diphenylquinone, thiopyrandioxide, carbodimide, fluorenylidenemethane, distyrylpyrazine,naphthalene, aromatic ring tetracarboxylic acid anhydrides such asperylene, metal complexes represented by metal complexes such asphthacyanine and 8-quinolinol derivatives and metal complexes comprisingmetal phthalocyanine, benzoxazole or benzothiazole as a ligand, organicsilanes, and derivatives of the foregoing compounds. Though the filmthickness of the electron injection layer and the electron transportlayer is not particularly limited, in general, it is preferably in therange of from 1 nm to 5 μm, more preferably in the range of from 5 nm to1 μm, and further preferably in the range of from 10 nm to 500 nm. Eachof the electron injection layer and the electron transport layer may beof a single layer structure made of one or two or more kinds of theforegoing materials, or may be of a multilayered structure comprising aplurality of layers of the same formulation or a different formationfrom each other.

Examples of the formation method of the electron injection layer and theelectron transport layer include a vacuum deposition method, an LBmethod, a method of coating a solution or dispersion of the foregoingelectron injection/transport material in a solvent, an inkjet method, aprinting method, and a transfer method. In the case of the coatingmethod, the electron injection/transport material can be dissolved ordispersed together with a resin component. Examples of the resincomponent include those enumerated above for the holeinjection/transport layer.

As materials of the protective layer, any materials having a function toretard the matter that substances of likely promoting degradation of thedevice, such as water and oxygen, enter the device are employable.Specific examples include metals (such as In, Sn, Pb, Au, Cu, Ag, Al,Ti, and Ni), metal oxides (such as MgO, SiO, SiO₂, Al₂O₃, GeO, NiO, CaO,BaO, Fe₂O₃, Y₂O₃, and TiO₂), metal fluorides (such as MgF₂, LiF, AlF₃,and CaF₂), nitrides (such as SiN_(x) and SiO_(x)N_(y)), polyethylene,polypropylene, polymethyl methacrylate, polyimides, polyureas,polytetrafluoroethylene, polychlorotrifluoroethylene,polydichlorodifluoroethylene, a copolymer of chlorotrifluoroethylene anddichlorodifluoroethylene, copolymers obtained by copolymerizing amonomer mixture of ethylene and at least one comonomer,fluorine-containing copolymers having a cyclic structure in thecopolymerization main chain, water absorbing substances having acoefficient of water absorption of 1% or more, and moisture-proofingsubstances having a coefficient of water absorption of not more than0.1%.

The formation method of the protective layer is not particularlylimited. Examples include a vacuum vapor deposition method, a sputteringmethod, a reactive sputtering method, an MBE (molecular beam epitaxy)method, a cluster ion beam method, an ion plating method, a plasmapolymerization method (high-frequency ion plating method), a plasma CVDmethod, a laser CVD method, a heat CVD method, a gas source CVD method,a coating method, a printing method, and a transfer method.

EXAMPLES

The invention will be described below in more detail with reference tothe Examples, but it should not be construed that the invention islimited thereto.

Example 1

A glass substrate having a size of 25 mm×25 mm×0.7 mm, on which ITO issubjected to film formation in a thickness of 150 nm (manufactured byTokyo Sanyo Vacuum Co., Ltd.) is used as a transparent supportingsubstrate. This transparent supporting substrate is etched and rinsed.On this ITO glass substrate, Baytron P (a PEDOT-PSS(polyethylenedioxythiophene-polystyrenesulfonic acid doped material)dispersion, manufactured by Bayer AG) is spin coated and then dried invacuo at 100° C. for one hour, thereby providing a hole transport layer(film thickness: about 100 nm). Forty milligrams ofpoly-N-vinylcarbazole (PVK) as a hole transport compound, 1 mg of aphosphorescent compound G-1 (Ir(ppy)₃), and 6 mg of an electrontransport compound ET-1 are dissolved in 3.8 g of chloroform, and thesolution is spin coated on the forgoing substrate (film thickness: about50 to 70 nm), followed by drying in vacuo at 100° C. for 30 minutes. Theresulting substrate is subjected to vapor deposition with an electrontransport material ET-2 and LiF in that order in a film thickness ofabout 36 nm and about 1 nm, respectively under vacuum of 10⁻³ to 10⁻⁴ Paunder the condition at the substrate temperature of room temperature. Apatterned mask (luminescent area: 5 mm×4 mm) is placed thereon andsubjected to vapor deposition with aluminum in a film thickness of about200 nm, to prepare a device. Incidentally, the thus prepared device issealed within a dry glove box.

Example 2

A device is prepared in the same manner as in Example 1, except that inthe device of Example 1, the electron transport material ET-1 to beadded in the luminescent layer is replaced by ET-2.

Example 3

A device is prepared in the same manner as in Example 1, except that inthe device of Example 1, G-1 is replaced by G-2 and that in the electrontransport layer to be vapor deposited, ET-2 is replaced by ET-1.

Comparative Example 1

A device is prepared in the same manner as in Example 1, except that inthe device of Example 1, the electron transport material ET-1 to beadded in the luminescent layer is not added.

Comparative Example 2

A device is prepared in the same manner as in Example 1, except that inthe device of Example 1, the electron transport material ET-1 to beadded in the luminescent layer is replaced by PBD, and G-1 is replacedby G-2 and that in the electron transport layer to be vapor deposited,ET-2 is replaced by ET-1.

The luminescence wavelength and external quantum efficiency of each ofthe devices used in the Examples and Comparative Examples aredetermined. That is, a direct current constant voltage is applied toeach device to cause light emission using a source measure unit 2400manufactured by Toyo Corporation. The luminance is measured using aluminance meter BM-8 manufactured by Topcon Corporation, and theluminescence wavelength and CIE chromaticity coordinate are measuredusing a spectral analyzer PMA-11 manufactured by Hamamatsu PhotonicsK.K. The external quantum efficiency is calculated based on theresulting numerical values according to the luminance reduction method.The results obtained are summarized in the following table. TABLE 1Luminescent layer External Luminance Electron Electron Luminescencequantum upon Host Guest transport transport wavelength efficiencymeasurement compound compound material layer (nm) (%) (cd/m²) Example 1PVK G-1 ET-1 ET-2 515 16.8 88 Example 2 PVK G-1 ET-2 ET-2 515 10.6 107Comparative PVK G-1 Nil ET-2 515 6.9 127 Example 1 Example 3 PVK G-2ET-1 ET-1 462 9.2 94 Comparative PVK G-2 PBD ET-1 462 1.3 109 Example 2

Further, the T₁ energy level values of the respective compounds areshown in the following table. TABLE 2 T₁ level Compound (kcal/mole) ET-168 ET-2 60 PBD 55 PVK 65 G-1 60 G-2 65

Example 4

The device of Example 3 and the device of Comparative Example 1 wereeach light emitted at 300 cd/m² and measured for luminance half-life.The device of Example 3 had a half-life of about 2 times that of thedevice of Comparative Example 1.

Example 5

TPD (N,N′-diphenyl-N,N′-di(o-tolyl)benzidine) was vapor deposited in athickness of 50 nm on an ITO substrate, on which were then vapordeposited jointly A-10 (the compound of the invention, T₁=65 kcal/mole)and ET-1 (the compound of the invention) and G-2 (the compound of theinvention, T₁=65 kcal/mole) in a weight ratio of 65/35 in a thickness of36 nm. ET-1 (the compound of the invention) was further vapor depositedthereon in a thickness of 36 nm. A cathode was vapor deposited in thesame manner as in Example 1, to prepare a device. As a result ofevaluation, blue luminescence of ELmax=465 nm was obtained in anexternal quantum efficiency of 12%.

Example 6

A device was prepared in the same manner as in Example 1, except forusing B-68 (T₁=60 kcal/mole) in place of ET-1 and using G-1 in place ofG-2, and then evaluated. As a result, green luminescence of ELmax=520 nmwas obtained in an external quantum efficiency of 18%.

Comparative Example 3

Forty milligrams of PVK, 12 mg of PBD, and 1 mg of G-1 (T₁=60 kcal/mole)were dissolved in 2.5 mL of dichloroethane, and the solution was spincoated on an ITO substrate (at 2,000 rpm for 20 seconds). A cathode wasvapor deposited in the same manner as in Example 1, to prepare a device.As a result of evaluation, green luminescence of ELmax=515 nm wasobtained in an external quantum efficiency of 3%.

Comparative Example 4

A device was prepared using the green luminescent material G-1 in placeof a red phosphorescent material (PtOEP) of red EL device as describedin Example 3 of JP-A-2002-305085. Copper phthalocyanine was vapordeposited in a thickness of 20 nm on an ITO substrate, on which was thenvapor deposited α-NPD (N,N′-diphenyl-N,N′-di(α-naphthyl)-benzidine) in athickness of 30 nm. Further, BAlq₂(bis(8-hydroxy-2-methylquinolinato)-biphenyloxy-aluminum complex, T₁=notmore than 55 kcal/mole), α-NPD (Ip=5.5 eV, T₁=not more than 57kcal/mole), and G-1 were vapor deposited thereon jointly in a weightratio of 20/80/4. BAlq₂ was further vapor deposited thereon in athickness of 10 nm, on which was then vapor deposited Alq (tris(8-hydroxyquinolinato) aluminum complex) in a thickness of 40 nm.Thereafter, a cathode was vapor deposited in the same manner as inExample 1, to prepare a device. As a result of evaluation, greenluminescence of ELmax=515 nm was obtained in an external quantumefficiency of 6%.

Comparative Example 5

A device was prepared in the same manner as in Comparative Example 4,except for using a blue luminescent material G-2 in place of G-1, andthen evaluated. As a result, blue luminescence of ELmax=465 nm wasobtained in an external quantum efficiency of 3%.

Comparative Example 6

Copper phthalocyanine was vapor deposited in a thickness of 10 nm on arinsed ITO substrate, on which NPD was vapor deposited in a thickness of50 nm. Then, on the NPD layer, was then vapor deposited one of thecompounds of the invention, CBP (T₁=60 Kcal/mol) and Ir(ppy)₃ (T₁=60Kcal/mol) in a mass ratio of 17:1 in a thickness of 36 nm. Further, onthis layer, one of the compounds of the invention, ET-2 (T₁=60 Kcal/mol)was vapor deposited in a thickness of 36 nm. Thereafter, a cathode wasvapor deposited in the same manner as in Example 1, to prepare a device.As a result of evaluation, green luminescence of ELmax=515 nm wasobtained in an external quantum efficiency of 5%.

Example 7

Instead of CBP, a mixture of compounds of the invention A-28 (anelectron injection/transport compound, T₁=65 Kcal/mol) and C-12 (a holeinjection/transport compound, T₁=62 Kcal/mol) in the mass ratio of 1:1was used for the preparation of a device in the same way as inComparative Example 6. As a result of the evaluation of the device thusprepared, green light emission originating from Ir(ppy)₃ was obtained atELmax=515 nm. And an external quantum efficiency of 8% was obtained. Theoperating durability at 500 cd/m² was evaluated to give a half decaytime of about 4 times as long as that of the device in ComparativeExample 6.

Example 8

Instead of CBP, a mixture of ET-2 (an electron injection/transportcompound) and CBP (a hole injection/transport compound) in the massratio of 1:10 was used for the preparation of a device in the same wayas in Comparative Example 6. As a result of the evaluation of the devicethus prepared, green light emission originating from Ir(ppy)₃ wasobtained at ELmax=515 nm. And an external quantum efficiency of 7% wasobtained. The operating durability at 500 cd/m² was evaluated to give ahalf decay time of about 3 times as long as that of the device inComparative Example 6.

Example 9

Instead of CBP, a mixture of C-18 (an electron injection/transportcompound, T₁=65 Kcal/mol) and C-12 (a hole injection/transport compound,T₁=62 Kcal/mol) in the mass ratio of 1:1 was used for the preparation ofa device in the same way as in Comparative Example 6. As a result of theevaluation of the device thus prepared, green light emission originatingfrom Ir(ppy)₃ was obtained at ELmax=515 nm. And an external quantumefficiency of 6% was obtained. The operating durability at 500 cd/m² wasevaluated to give a half decay time of about twice as long as that ofthe device in Comparative Example 6.

Example 10

Instead of CBP, a mixture of C-22 (an electron injection/transportcompound, T₁=68 Kcal/mol) and C-12 (a hole injection/transport compound,T₁=65 Kcal/mol) in the mass ratio of 1:2 was used for the preparation ofa device in the same way as in Comparative Example 6. As a result of theevaluation of the device thus prepared, green light emission originatingfrom Ir(ppy)₃ was obtained at ELmax=515 nm. And an external quantumefficiency of 7% was obtained. The operating durability at 500 cd/m² wasevaluated to give a half decay time of about 3 times as long as that ofthe device in Comparative Example 6.

Example 11

On a rinsed ITO support, copper phthalocyanine was vapor deposited in athickness of 10 nm, on which NPD was vapor deposited in a thickness of50 nm. On the layer thus prepared, a compound of the invention C-12 (ahole injection/transport compound, T₁=62 Kcal/mol) and Ir(ppy)₃ at themass ratio of 17:1 were vapor deposited in a thickness of 1 nm.Thereafter A-28 (an electron injection/transport compound, T₁=65Kcal/mol) and Ir(ppy)₃ were vapor deposited at the mass ratio of 17:1 ina thickness of 1 nm. This cycle was repeated 18 times to provide aluminescent layer of about 36 nm thickness. By vapor depositing ET-2 ina thickness of 36 nm on this luminescent layer, a device was prepared inthe same manner as in Comparative Example 6. As a result of theevaluation of the device thus obtained, green light emission originatingfrom Ir(ppy)₃ was obtained at ELmax=515 nm. And an external quantumefficiency of 8% was obtained. The operating durability at 500 cd/m² wasevaluated to give a half decay time of about 5 times as long as that ofthe device in Comparative Example 6.

From the foregoing results, it is noted that the devices according tothe invention, in which an electron transport material having a high T₁value is added in the luminescent layer, have a high external quantumefficiency as compared with the devices in which PBD is added in theluminescent layer and those in which only two kinds of compounds arecontained in the luminescent layer. Also, the devices according to theinvention in which the energy level is regulated can realize blue and/orgreen light emission with high-efficiency luminescence.

According to the invention, it is possible to provide a luminescentdevice that can realize green or blue light emission, has high luminanceand high external quantum efficiency and has excellent durability.

This application is based on Japanese Patent application JP 2002-381014,filed Dec. 27, 2002, and Japanese Patent application JP 2003-409183,filed Dec. 8, 2003, the entire contents of those are hereby incorporatedby reference, the same as if set forth at length.

1. An organic electroluminescent device comprising: a pair ofelectrodes; and at least one organic layer between the pair ofelectrodes, the at least one organic layer including a luminescentlayer, wherein the luminescent layer contains at least one electroninjection/transport compound, at least one hole injection/transportcompound, and at least one green or blue phosphorescent compound; andthe electron injection/transport compound and the holeinjection/transport compound each has a minimum triplet exciton energyvalue which is equal to or more than that of the green or bluephosphorescent compound.
 2. The organic electroluminescent device ofclaim 1, wherein the hole injection/transport compound has an ionizationpotential of from 5.6 eV to 6.1 eV.
 3. The organic electroluminescentdevice of claim 1, wherein the electron injection/transport compound hasan electron affinity of from 2.0 eV to 3.5 eV.
 4. The organicelectroluminescent device of claim 1, wherein the green or bluephosphorescent compound is a transition metal complex capable ofemitting light via a triplet excitation state.
 5. The organicelectroluminescent device of claim 1, wherein the electroninjection/transport compound, the hole injection/transport compound andthe green or blue phosphorescent compound each has a T₁ value of 62kcal/mole or more; and phosphorescence obtained from the green or bluephosphorescent compound has a λmax of not longer than 500 nm.
 6. Theorganic electroluminescent device of claim 1, wherein the holeinjection/transport compound is a substituted or unsubstituted pyrrolecompound.
 7. The organic electroluminescent device of claim 6, whereinthe substituted or unsubstituted pyrrole compound is represented by theformula (1):

wherein R¹¹ to R¹⁵ each represents a hydrogen atom or a substituent, andthe substituents may be bonded to each other to form a ring structure.8. The organic electroluminescent device of claim 7, wherein the formula(1) is represented by the formula (3):

wherein R³² to R³⁵ each represents a hydrogen atom or a substituent, andthe substituents may be bonded to each other to form a ring structure;L³¹ represents a connecting group; L³² represents a di- or more valentconnecting group; n³¹ represents an integer of 2 or more; and n³²represents an integer of from 0 to
 6. 9. The organic electroluminescentdevice of claims 1, wherein the electron injection/transport compound isa heterocyclic compound containing at least two nitrogen atoms.
 10. Theorganic electroluminescent device of claim 9, wherein the heterocycliccompound containing at least two nitrogen atoms is a compoundrepresented by the formula (2):

wherein R²¹ represents a hydrogen atom or a substituent; X²¹, X²², X²³,and X²⁴ each represents a nitrogen atom or a substituted orunsubstituted carbon atom; and at least one X²¹, X²², X²³, and X²⁴represents a nitrogen atom.
 11. The organic electroluminescent device ofclaim 10, wherein the formula (2) is represented by the formula (4):

wherein R⁴¹, R⁴², and R⁴³ each represents a hydrogen atom or asubstituent; L⁴¹ represents a connecting group; n⁴¹ represents aninteger of 2 or more; L⁴² represents a di- or more valent connectinggroup; and n⁴² represents an integer of from 0 to
 6. 12. The organicelectroluminescent device of claim 10, wherein the formula (2) isrepresented by the formula (5):

wherein R⁵², R⁵³, and R⁵⁴ each represents a hydrogen atom or asubstituent; L⁵¹ represents a connecting group; n⁵³ represents aninteger of 2 or more; L⁵² represents a di- or more valent connectinggroup; and n⁵² represents an integer of from 0 to 6.